The use of elemental fluorine as fluorinating agent for the preparation of fluorinated compounds is well known, see for instance HUTCHINSON, John, et al. Elemental Fluorine in Organic Chemistry. Topics in Current Chemistry. 1997, vol. 193, p. 1-43.
Addition of elemental fluorine to carbon-carbon double bonds has been previously described: see for example HUTCHINSON, John, et al. Elemental Fluorine in Organic Chemistry. Topics in Current Chemistry. 1997, vol. 193, p. 1-43; SANDFORD, Graham. Elemental Fluorine in Organic Chemistry (1997-2006). J. Fluorine Chem. 2007, vol. 128, p. 90-104.
Many olefins, including haloolefins, are readily available in commercial quantities, thus the fluorination of olefins to produce fluorinated saturated products would be commercially useful. However, the fluorination reaction of unsaturated compounds is highly exothermic and violent in nature. The high exothermicity of the reaction can lead to strong increases of the reaction temperature, within very short times, and is therefore difficult to control. Locally the temperature can be so high as to cause the scission of carbon-carbon bonds, leading to the formation of undesired by-products. Another occurring drawback of the direct addition of fluorine to olefins is the dimerization of the reaction product.
To control the reaction, the fluorination of olefins has been typically carried out at a very low temperature, in the presence of a solvent and with a very low concentration of elemental fluorine, heavily diluted with an inert gas. This process suffers from low productivity without significant alteration of the fluorination mechanism; in other words, selectivity in the fluorine addition product tends to remain low. See for instance, CONTE, L., et al. Fluorination of hydrogen-containing olefins with elemental fluorine. Journal of Fluorine Chemistry. 1988, vol. 38, p. 319-326. wherein the reaction of addition of fluorine to chloroolefins was carried out employing very low concentrations of fluorine in the presence of apolar solvents resulting in low selectivity in the addition product.
Alternatively, control of the fluorine addition process has been disclosed in EP 396168 A (PCR, INC.) Jul. 11, 1990 by carrying out the reaction in an eductor, i.e. a jet pump that allows addition of fluorine at very high flow rates, thereby promoting rapid circulation of the reaction mixture in the cooling system. The rapid circulation of the reaction fluids prevents the formation of hot-spots as well as the occurrence of side-reactions.
There is thus still a need in the art for a process for addition of fluorine to olefins, in particular haloolefins, providing high yields and productivity. Additionally, there is still a need for a process providing high yields and productivity without requiring the use of complex equipment.